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Submerged Tunnel:

What is this???:

A Submerged Tunnel is a tunnel that floats in water, supported by its buoyancy(specifically , by employing the hydrostatic thrust, or Archimedes' Principle ). The tube is placed underwater, deep enough to avoid water traffic and weather, but not so deep that high water pressure needs to be dealt with— usually 20–50 m (60–150 ft.) is sufficient. Cables either anchored to the Earth or to pontoons at the surface prevent it from floating to the surface or submerging, respectively. What is this???

Why this ?????:

The big advantage of a floating submerged tunnel compared to a bridge is the lightly loaded construction . Under water a weight reduction takes place which lowers the loads to be carried by the tunnel. Flexible submerged tunnel has much less problems with earthquakes which can happen in this area. F loating tunnel can be built fast from both shores having no problems with wind or high seas . Why this ?????

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Facts.. Submerged tunnels do not suit every situation. However, if there is water to cross, they usually present a feasible alternative to bored tunnels at a comparable price, and they offer a number of advantages, such as: Submerged tunnels do not have to be circular in cross section. Almost any cross section can be accommodated, making Submerged tunnels particularly attractive for wide highways and combined road/rail tunnels. Some examples of realized cross sections are shown below……………

Submerged tunnels can be placed immediately beneath a waterway. In contrast, a bored tunnel is usually only stable if its roof is at least its own diameter beneath the water. This allows Submerged tunnel approaches to be shorter and/or approach gradients to be flatter - an advantage for all tunnels, but especially so for railways. :

Submerged tunnels can be placed immediately beneath a waterway. In contrast, a bored tunnel is usually only stable if its roof is at least its own diameter beneath the water. This allows Submerged tunnel approaches to be shorter and/or approach gradients to be flatter - an advantage for all tunnels, but especially so for railways .

Regular vs. Underwater Tunnels:

How this is constructed…….:

A trench is dredged in the bed of the water channel. How this is constructed…….

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Tunnel elements are constructed in the dry, for example in a casting basin, a fabrication yard, on a ship-lift platform or in a factory unit. casting basin fabrication yard ship-lift platform factory unit

After Casting…..:

After Casting….. After casting the ends of the element are then temporarily sealed with bulkheads. Each tunnel element is transported to the tunnel site - usually floating, occasionally on a barge, or assisted by cranes.

Installation of tunnel elements in the trench :

For transportation of the element from the flooded casting basin or dock to the tunnel trench, conventional towage is normally used. The warping, which ends with the tunnel element being moored for immersion, is normally carried out by the contractor's organisation responsible for the subsequent sinking and joining, whereas towing normally is done by experienced towage companies. The immersion of the tunnel element is carried out after the tunnel element bas been moored and the element has been ballasted as necessary to provide adequate loads in the immersion tackles. Installation of tunnel elements in the trench

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The tunnel element is lowered to its final place on the bottom of the dredged trench.

The new element is placed against the previous element under water. Water is then pumped out of the space between the bulkheads. Water pressure on the free end of the new element compresses the rubber seal between the two elements, closing the joint. :

The new element is placed against the previous element under water. Water is then pumped out of the space between the bulkheads. Water pressure on the free end of the new element compresses the rubber seal between the two elements, closing the joint.

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Backfill material is p laced beside and over the tunnel to fill the trench and permanently bury the tunnel, as illustrated in the figures .

Approach structures can be built on the banks before, after or concurrently with the Submerged tunnel, to suit local circumstances. :

Approach structures can be built on the banks before, after or concurrently with the Submerged tunnel, to suit local circumstances.

ARE THERE ANY SPECIAL PROBLEMS ?:

ARE THERE ANY SPECIAL PROBLEMS ? Submerged tunnels are sometimes perceived by newcomers to the technology as "difficult" due to the presence of marine operations. In reality though, the technique is often less risky than bored tunnelling and construction can be better controlled. The marine operations, though unfamiliar to many, pose no particular difficulties.

The perceived problems include…:

DREDGING Dredging technology has improved considerably in recent years, and it is now possible to remove a wide variety of material underwater without adverse effects on the environment of the waterway. The perceived problems include…

INTERFERENCE WITH NAVIGATION Interference with navigation: On busy waterways, it is sometimes assumed that construction of an Submerged tunnel would be impractical as it would interfere with shipping. In fact, such tunnels have been successfully built in some exceptionally busy waterways without undue problems. :

INTERFERENCE WITH NAVIGATION Interference with navigation: On busy waterways, it is sometimes assumed that construction of an Submerged tunnel would be impractical as it would interfere with shipping. In fact, such tunnels have been successfully built in some exceptionally busy waterways without undue problems.